Method and apparatus for determining the position of a printed or written item with respect to an identification mark applied thereto



Aug. 2, 1960 K. STEINBUCH 2,947,972

METHOD AND APPARATUS FOR DETERMINING THE PQSITION OF A PRINTED ORWRITTEN ITEM WITH RESPECT TO AN IDENTIFICATION MARK APPLIED THERETOFiled June 27, 195'! lengfh dimension of letter G? 4 3 low Pa. F/lfer I-0 v law Pass FI/zJer my Pass Fi/te'r 3 5 6 2 INVENTOR K. fitenbuckATTORNEY United States Patent METHOD AND APPARATUS FOR DETERMINING THEPOSITION OF A PRINTED OR WRITTEN ITEM WITH RESPECT TO AN IDENTIFICATIONMARK APPLIED THERETO Karl Steinbuch, Fellbach, Wurttemberg, Germany, as-

signor to International Standard Electric Corporation, New York, N.Y., acorporation of Delaware Filed June 27, 1957, Ser. No. 668,502

- Claims priority, application Germany July 7, 1956 2 Claims. (Cl.340-149) The present invention relates to a method of and apparatus fordetermining the position or orientation of a printed or written itemwith respect to an identification mark applied thereto. This problemespecially arises e.g. with letters, bank accounting cheques, bank notesand the like, which are required to be sorted with respect to theirplaces of destination or receipt. A particular need for such a methodexists in a post ofiice for the sorting of mail items. The descriptionof the instant invention therefore, is particularly directed to a methodof recognizing the position of mail items, but the invention is notrestricted to such application.

in order to enable a sorting of items it is required that the respectiveletters, cards or the like are led past the sorting operator in areadable manner. However, since the items on the conveyor belt, on whichthey are led past the operator, may be lying in different positions itis rendered necessary to turn the non-readable items accordingly. Thenumber of possible positions is limited to four assuming that a suitabledevice ensures that the longest edges of the items on the conveyingsystem always lie horizontally, so that turns of 90 are practicallyexcluded.

lostage stamps may be regarded as a characteristical identification markfor letters. Furthermore, it may be assumed that in the readableposition of the letters the stamps are stuck to the front of theenvelope in the right-hand upper corner. For determining the position ofthe letters it is, therefore, necessary to examine the right-hand uppercorner of the letter. The result of such an examination is then utilizedfor controlling the following operation, in the course of which theletters, etc. are sorted in accordance with their respective positions.

it is possible to carry out the examination with respect toidentification marks on written or printed items by means of variousmethods employing a photo-electric scanning or sensing. One methodconsists in transporting the items past a scanning or sensing devicecontinuously on a conveyor belt systems, e.g. of the edgewise type, andmoving a scanning beam up and down vertically in relation to thedirection of movement. As soon as the identification mark is hit by thebeam, intensity fluctuations will be caused in a photocell which then,via amplifiers, can be used to produce a control pulse. Depending onwhether the fluctuations of intensity appear when sweeping over theupper or lower half of the letter this pulse is utilized for a sortingoperation with a subsequent turning of the item or letter, or for asorting operation without involving a turning of the letter.

Such examination methods, however, are easily liable to mistakes orerrors, because on the items there may also be other markings or signs,such as remarks with respect to the address or sender, or the like, andwhich, under certain circumstances, may cause a similar intensity Anobject of the present invention is to avoid such" faulty evaluations.According to the instant invention the mean value of a signal portion,derived from the identification mark, is compared with a fixed orpredetermined threshold value which is determined in such a way thatwhen exceeding the threshold value, there can be made certainconclusions as to the location of the identification mark. For thescanning of the examination range there may be used a plane-likeexploring photocell. However, since in some cases the scanning devicewill also have to serve the evaluation of narrow ranges, such as at theevaluation of the white edges of the postage stamps in the case ofdark-colored letters, it is of advantage to employ a gap-type photocell.In such a case, however, it is necessary to provide for means enablingthe examination of a complete identification-mark range. On the otherhand, also in the case of gap scanning, all transitions in brightness,which are caused by recordings, such as writing, are evaluated as well,so that there arises the additional problem of how to exclude orsuppress the larger signals resulting from the scanning of writing orthe like.

According to the present invention the above problem is solved byfeeding the signals coming from the photocell simultaneously to ahighpass and a low-pass filter with parallel-connected inputs. Theoutput signals from the high-pass filter are rectified and are fed to asecond low-pass filter and the output signals from the two lowpassfilters are then subtracted one from the other. This may be accomplishedin that the rectifier only permits the passage of the negative signalportions and in that these negative signals, after having passed throughthe second low-pass filter, are added to the positive signals from thefirst low-pass filter. in this way the signals resulting from thescanning of the writing, etc., will be completely or almost completelycompensated, while an unambiguous identification signal will remain,which is capable of being well compared with a predetermined thresholdvalue.

in the following, the invention will be particularly described withreference to the accompanying drawings and the example of determiningthe location of a postage stamp on a letter (envelope).

in the drawings: I

Fig. 1 shows a photocell signal produced by the scanning of a letter inreadable position;

Fig. 2 shows a circuit arrangement for carrying out the method accordingto the invention, and

Pig. 3 shows three diagrams of the signals produced in the individualstages of the arrangement according to Fig. 2.

The letters travel continuously past the scanning device of an edgewayconveyor belt, whereby a photocell signal is produced as is shown inFig. l. The intensity peaks in front of the wide or broad signal, whichcorresponds to the postage stamp, are caused by the writing or othermarkings on the front of the letter. (In all of the wave form diagramsit is assumed that the abscissa corresponds to the white-value, and thatwith an increasing ordinate value the signal approaches theblack-value.)

The postage stamp signal, as will be seen from Fig. 1, consists of arelatively large direct-current portion, whilst over the remaining partsof the letter the peaks are much narrower. This difference, therefore,may be used for identifying the location of the stamp. A simpleexpedient is to fix a value lying between the two directcurrent valuesto be expected, so that when this value is exceeded, this indication maybe used to deduce the location of the stamp. The threshold value can bedetermined the better the greater the difference is between the twodirect-current portions. Therefore, care should be taken that thesignals produced by the writing or other extraneous markings aresuppressed as far as possible, whereby the direct-current portion ofthese parts of the letter becomes substantially smaller and, in certaincases,

even zero.

Referring to Fig. 2 there is shown an arrangement for forming the peakvalue by simultaneously excluding the signals produced by the writing orthe like. The photocell signal produced by the scanning operation of thegap photocell 1, after being amplified in the amplifier 2, issimultaneously fed to the high-pass filter 3 and to the low-pass filter4. The low-pass filter is adapted to smooth the curve, so that thesignals caused by the writing on the letter are largely suppressed. Theoutput signal of the low-pass filter 4 is shown in Fig. 3a. Actuallythis signal could itself be used for comparison with the thresholdvalue, but the difference between the stamp portion and the remainingportions of the letter is too small, and may even entirely disappear insome specially unfavorable cases. For this reason the scanning signal issimultaneously fed to the high-pass filter 3, at the output of whichthere appear the higher-frequency signals, as shown in Fig. 3b of thedrawings. These signals are then rectified by the rectifier 5, so thatonly the negative portion of the signal is permitted to pass. The thusrectified signals are then fed to another low-pass filter 6, similar tothe low-pass filter 4, and thereby smoothed. The output signals of thelow-pass filter 6 are shown in Fig. 3c. Thereupon the output signalsfrom the two lowpass filters 4 and 6 are algebraically added in thecombining circuit 7. An illustration of this adding circuit is shown onpage 458 of Reference Data for Radio Engineers, 4th edition, copyrightedby I.T.&T., 1956. As will be seen from the Figs. 3a and 3c the signalsproduced by the writing will be compensated either entirely or almostcompletely on account of the combining process, so that one of thedirect-current portions will disappear. In this way there will remain adistinctly wide signal for identifying the stamp location, thedirect-current value of which can be well defined with respect to apredetermined threshold value. An example of this threshold comparatoris shown on page 329 Fig. 9.3a in volume 19 of the Radiation LaboratorySeries. The difference signal is fed to a comparing device 8(comparator), in which it will be compared with the said thresholdvalue. By noting when the threshold value is exceeded, conclusions maybe drawn as to the position of the postage stamp. When the thresholdvalue is thus exceeded there is produced a control signal which may beused to initiate the required controlling operations for handling thescanned letter. Four photocells may be used which simultaneously scanboth sides of the letter and the upper and lower halves of each side. Inthis case that particular photocell which locates the postage stamp thenproduces the control signal which initiates the desired controllingoperation to direct the letter into a filing compartment, or the like.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention.

What is claimed is:

1. System for determining the position of a written or printed item withrespect to the location thereon of an identification mark appliedthereto, comprising photoelectric scanning means, the item being movedrelative to said scanning means whereby at least a portion of thesurface of said item is scanned, means for deriving a signal currentfrom said scanning means, threshold circuit means including a referencesource of current having a predetermined value for comparing said signalcurrent with said reference current, said threshold circuit comprising aparallel branch circuit intermediate said scanning means and said meansfor deriving a signal current from said scanning means, said branchcircuit comprising means for cancelling signals derived from markings onsaid item not corresponding to said identification mark, whereby thelocation of said identification mark may be deduced when the currentderived from said threshold circuit differs from said reference currentby a predetermined amount.

2. System according to claim 1, wherein said parallel branch circuitcomprises a first low-pass filter and a high-pass filter the inputs ofwhich are connected in parallel, means for applying said signal currentto said inputs, a rectifier, a second low-pass filter, means forserially connecting said high-pass filter, said rectifier and saidsecond low-pass filter in the order named, a combining circuit, meansconnecting the outputs of both said low-pass filters to said combiningcircuit, and means connecting the output of said combining circuit tosaid comparator.

Hansell Apr. 23, 1940 Zworykin Nov. 4, 1952

